1. Field of the Invention
The invention relates generally to rotary drilling systems, and more specifically to drive steel improvements for drilling systems as used in drilling and boring for roof bolting operations for tunnel construction, mining and the like.
2. Description of the Prior Art
In the fields of industrial, mining and construction tools, polycrystalline diamond (PCD) is now in wide use in making cutting tool inserts, sometimes called polycrystalline diamond compacts (PDC). PCD materials are formed of fine diamond powder sintered by intercrystalline bonding under high temperature/high pressure diamond synthesis technology into predetermined layers or shapes; and such PCD layers are usually permanently bonded to a substrate of “precemented” tungsten carbide to form such PDC insert or compact. The term “high density ceramic” (HDC) is sometimes used to refer to a mining tool having a PCD insert. “Chemical vapor deposition” (CVD) and “Thermally Stable Product” (TSP) diamond-forms may be used for denser inserts and other super abrasive hard surfacing and layering materials, such as layered “nitride” compositions of titanium (TiN) and carbon (C2N2) and all such “hard surface” materials well as titanium carbide and other more conventional bit materials are applicable to the present invention.
The principal types of drill bits used in rotary drilling operations are roller bits and drag bits. In roller bits, rolled cones are secured in sequences on the bit to form cutting teeth to crush and break up rock and earth material by compressive force as the bit is rotated at the bottom of the bore hole as in mining operations. In drag bits, PCD or like cutting elements on the bit act to cut or shear the earth material. The action of some flushing fluid medium, such as fluid drilling mud, water or a compressed air/vacuum system, is important in all types of drilling operations to cool the cutting elements and to flush or transport cuttings away from the cutting site. It is important to remove cuttings from the hole to prevent accumulations that may plug water passages and otherwise interfere with the crushing or cutting action of the bit; and the cooling action is particularly important in the use of PCD/CVD/TSP cutters to prevent carbon transformation of the diamond material.
Roof drill bits are one form of a rotary drag bit used in roof bolting operations, which are overhead so the drilling operation is upward through earth structures of extremely hard rock or mineral (coal) deposits; and stratas of shale, loose (fractured) rock and mud layers are frequently encountered.
My prior U.S. Pat. Nos. 5,180,022; 5,303,787 and 5,383,526 disclose substantial improvements in HCD roof drill bits using PCD cutting elements constructed in a non-coring arrangement, and also teach novel drilling methods that greatly accelerate the speed of drilling action and substantially reduce bit breakage and change-over downtime. These prior HCD bits easily drill through most earth structures, but it was discovered that some drill bits might plug when drilling through mud seams and other soft earth formations and my prior U.S. Pat. No. 5,535,839 is a coring-type bit designed for such earth structures.
Also in the past, the use of large quantities of drilling fluids for overhead irrigation resulted in uncontrolled water loss and floor flooding. It was determined that the amount of water required to wet drill with PCD rotary bits could be reduced from a conventional (tungsten carbide bit) range of 9-18 gallons per minutes down to about 1-3 quarts per minute when atomized into an air mist on PCD inserts. My U.S. Pat. No. 5,875,858 discloses a compressor and air-water mixing system that greatly reduces the amount of water required for effective hole flushing while substantially reducing the amount of respirable dust. My U.S. Pat. No. 6,092,612 discloses rotary drilling systems including improvements in drive steel columns and secondary bore reamers to ensure delivery of flushing fluid and effective bit and reamer cooling without substantial pressure loss, and especially using the low volume air mist system of my earlier work. The disclosures these prior U.S. Pat. Nos. 5,875,858 and 6,092,612 are incorporated herein by reference as though fully set out.
One prior and continuing problem involves the connection of the drive steel to the chuck of a drilling machine. The continuing practice in the industry typically utilizes a connector on the tubular drill steel end with a flanged end to seat in the machine chuck; and such connectors are fastened on the drill steel using one of the following techniques:                (1) a connector shank is forged onto the round drill steel with the potential problems of (a) being off center, (b) too high or low forging temperature, and (c) improper re-tempering; and, in addition, forged drill steel is relatively expensive and labor intensive;        (2) a connector is welded onto thin walled round or hex drill steel which may break due to fatigue and failure resulting from metal softening in the welded area (this practice has been banned in some jurisdictions due to injuries);        (3) a connector is press fit into a machined hex drill steel with the potential problems of (a) off center tapering and (b) loosening due to metal flow; or        (4) hex drill steel rods are cut to length and a chuck connector is inserted into a drilled rod end with the problems of (a) drill steel softness in the range of 28-35 Rc resulting in bending and also mushrooming on the machine chuck, (b) loosening and pulling apart of the connector, and (c) not being water tight for wet drilling or air tight with loss of vacuum when drilling dry.        
My U.S. Pat. No. 6,161,635 approaches this problem by providing a chuck adapter sealed on the end of the starter steel by fastening means including epoxy and cross-pinning attachment. However, it has been found that, even with O-ring and silicon sealant applied to such a “pin on” shank, such a shank adapter connection still develops leaks after extended use. This, of course, compromises that delivery of pressurized flushing fluid to the remote drilling bit end of the drill steel column.